Frequency control system



Patented Aug. 21, 1945 e assaooss` y i FREQUENCY CONTROL SYSTEM William `S. Marks, Jr., Long Branch, J.; ApplicationNoveiber s, 1,942, serial iso; 464,755

` 4 claims. (o1. 25a-3s) (Granted under theeact of March 3, 1883, as

amendedApril 30, 1928; 370 0. G. 757) Theinvention'described herein may bev manufactured and used by or for` the Government for i governmental purposes, without the `payment to me of any royalty thereon. y e

yThis invention 4relates to a. radio frequency -wave generating system `and more particularly to a 'system for deriving aw series of' stable frequencies to be used for transmitter excitation andv related purposes. y

, Transmttersby which a. series of waves of diierent frequencies are propagated often incorporate therein a plurality ofV crystals serving to control oscillator stages so as to stabilize the output ofv the transmitter at each particular frequency thereof. Such transmitters ordinarily employ a separate crystal for each desired frequency inasmuch as the units of the desired frequenoy series are usually spaced from each other by comparativelysmall amounts and are not integral multiples `oi. the crystal frequency, If,for examples() frequencies were desired having the 'stabilityl of a "crystalcontrolled `oscillator and wherein said `:frequencies were spaced from each other by amounts apprecialb-ly smaller than that of thev crystalfrequency so that the umts of the series were not'integral multiplesof 4the crystal frequency, it would be Vordinarily necessary to employ substantially` 80 crystals `wherein each crystal controlled oscillator determined a particular frequency in the series. y

' Operations based upon the selection of harmonics of the crystallfrequency obviously cannot `satisfy `the requirements when frequencies spaced by amounts less than `that of the crystal frequency are desired. 'f y vThe use of va multivibrator to derive frequencies spaced by submultiples of `a crystal controlled oscillator is known but if it were desired to `derive a series of spaced frequencies in, forA example, the to2() megacycle `band,'an extremely high harmonic 'of the multivibratoroutput would have 'to beselected. Assuming that the multivibrator frequencyis 50 kilocyclesit would require at least the' 200th harmonic andfwould be impracticable 'for' an ordinary transmitter system.

Furthermore, in operating at these high order harmonics, therelative frequency separation becomes `increasingly smaller, andthe lsolator or illter circuits for selecting" the appropriate harmonies'inustfber extremely sharp and critical to distinguish between them. Such conditions are dilcult to., ineet due to the required delicacy '0f desi-sn and adjustment, "This dimculty is particularly` marked vin the use of remote control and push button tuning mechanism since slight irregularity in the transmission means such as may be `due to back lash inthe gears may detune the selector stages from the required setting.

` `Bearing the foregoing inmind, the present in vention is concerned with the provision of a series `of frequencies which are'contro'lled as to stability by the use Of a crystal controlled oscillator wherein a single crystal suiiicies to stabilize every unit frequency in theseries, 4which unit frequencies are notlimited to integral multiples of the crystal frequency. While a multivibrator is utilized in deriving frequencies spaced by a submultiple of the, crystal frequency, the present invention makes it unnecessary to employ unduly high harmonies of the multivibrator Voutput to attain relatively high frequencies.

` e frequencies-derived by the instant invention `are not only crystal controlled :but have no original` source of oscillations other than the crystalcontrolled oscillator so that variations in the `crystal controlled oscillatorcannot conflict 'with the frequencies from any other source to produce beat notes or other undesirable results. Since the original source is a single crystal controlled oscillator, `variations thereof are uniform throughout the system.` Such variations,V moreover, may be minimized by conventional means such as by thermostatic temperature control.

Y As is well-known,`cr`ystal controlled oscillators are often provided `with temperature control means to 4minimize frequency lvariations due to temperature changes. Crystals of different fre quencies mayrequire different conditions of such temperature control since crystals have individually varying 'temperature coefficients. In a transmitter having a large number of crystals, the problem is of considerable magnitude and is often partially solved by utilizing temperature control means adapted to all of the crystals involved. The tolerances thereof must be widened to accommodate allof the crystals and obviously cannot allow rigidcontrol Of'anyone of them. According to the present invention, however, such control may `be made as rigid as desired since `only one crystal is to be controlled 4bythe temperature control means.'

` Other andfurther "objects and advantages will bepointed out hereinafter and the novel features thereof `set forth in the appended claims.

In describing the details ofthe invention reference ismadeto thedrawing wherein:

Figure 1 is a blockdiagramillustrating an emvbodiment 4of the inventiom" and Figure 2 illustrates a" modification thereof.

Referring to Figure 1,the source of oscillaplier selector I2 which may be tuned to any The output of` multivibrator I I is connected to a selector or amone of a series of harmonics of the50 kilocycle multivibrator in a` dened lband width extending in frequency from 2 to 3 megacycles so 'that thek output of the selector I2 is 2.00 mc., 2.05 mc., 2.101:

mc., 2.15 mc., etc. up to 3.0 mc., representing, respectively, the 40th to 60th harmonic of the multivibrator II,

The4 desiredjharmonic is then selected and amplified in the amplifier selector I2 and, reptivity of the amplifier selector stage I2 need not be excessive since only .the 40th to the 60th harmonic of the multivibrator output is selected.

The output of channel A being in the 2 to 3 megacycle range, the nearest frequency to that of the desired one is spaced therefrom by at least two megacycles. As above stated, the selectivity of the mixer stage I3 need not be critical since it is only required to distinguish between widely separated frequencies. The system is therefore feasible where mechanical remote control or push button tuning means are used even should Athe tuning means employed cause deviation from the critical adjustment of the tuning units due to irregularities in the 'mechanical transmission.

y Figure 2 illustrates a modification of the in- 'I venticn. As an example of this modification,

' *the output of a 500 kilocycle crystal controlled resenting the output ofl channel A, is fed into a mi-Xer I3 where it is heterodynedin conventional mannerwith another frequency supplied by channel 1 3 of the system. .Y e

` Channel B includes a doubler I4 and a frequency multiplier I5, the combination of which serves to derive frequencies of 8,'9, 10, or 11' megacycles from the output of the oscillator stage I0. The doubler I4 raises the original frequency to twice its value, so that the multiplier I5 selects the 8th to the 11th Iharmonics ofthe output of the doubler I4', which harmonics are spaced by a full megacycle. p

The output of the frequency multiplier I5 is then fed into the mixer I3k whereit is heteroclyned with the output of the amplifier selector I2. The output of the mixer I3 is tuned to select the beat frequency produced, fory example, by the addition of the frequencies fed in by both channels. The output of mixer JI3' will therefore be in the 10 to 14 megacycle range, the particular outputfrequencies obtainable being spaced apart by 50 kilocycles throughout the range. Thus, any one of a series of 80 predetermined and uniformly spaced frequencies may be produced, al1 of which are crystal controlled .as to stability and are derivedfrom a single source,l but which are not necessarily integral multiples of the crystal frequency.

A particular advantage ofthe construction hereinabove set forth is the simplification of the mixer stage I3 made possible by the fact that a high degree of selectivity is not required andthe required selection is easily accomplished. This result is attributable to the fact that when the mixer I3 is tuned to select a specific beat frequency of the series, the nearest other frequency which is present in the mixer stage is removed from the desired frequency by a substantial amount. This amount is represented by the olitput frequency of the amplifier selector stage I2.

It will be noted that channel A, although providing thek source of sub-multiple differences, has an output which is appreciably'higher in frequency than that `of the crystal oscillator. This is of advantage effecting as it does a substantial. difference between the frequencies present in` the mixer stage I3. On the other hand, the output 'of channel A isof sufficiently low frequency s'o as not lto require relatively high harmonies of the multivibrator output. Thus, sufIicient excitation voltage for the selector stage I2 is provided. It' also follows that the -selecoscillator I6 feeds into and controls a multivibrator Il. The amplifier selector I8 is tunable to a frequency range of fromv 2 to 2.5 megacycles in steps of 50 kilocycles. The multivibrator II may operate, for example, at a fundamental frequency of 50 kilocycles so that the harmonic output frequencies of the amplifier selector I8 may be spaced 50 kilocycles apart.

Channel D includes a frequency multiplier I9 fed from the oscillator I6. Multiplier I9y may assume a conventional form and serves to vSelect the sixteenth to twenty-second harmonic of the 500 kilocycle initial crystal frequency. Fre,- quencies of 8, 8.5, 9, 9.5, 10, 10.5 and 11 are secured as desired and fed to the mixer 20 there to be heterodyned with the output of channel C. The output of mixer 20 is tunable to derive the desired additive frequencies in the range of l0 to 14 megacycle spaced 50'kilocyc1es apart.

Both systems hereinabove described are similar in that same output frequencies are secured therefrom, the difference being that in the example shown in Figure 2 the multivibrator channel need only cover a range of half Yal megacycle since the frequency multiplier channel 'i's divided into half megacycle differences within its range. Either system may be varied to derive wider or narrowerA bands with a greater or smaller numberof frequencies involved, or may employ different combinations to` derive the same frequencies, the examples given being illustrative of the utility and operation of the system. Both systems produce a large number 0f crystal controlled frequencies, which frequencies are not necessarily integral multiples of the single crystal employed.

The frequencies derived may be used for transmitter excitation or other purposes where a series of stable frequencies within a limited range are required. In the case of a transmitter, the crystal controlled oscillator may be phase or frequency modulated before being multiplied in either channel B or channel D. When the crystal controlled oscillator is phase or'frequency modulated befcre being multiplied, the invention presents particular ladvantages Y since thel frequency of the phasel or frequency modulated carrier wave may be increased or decreasedby beating it with the output' of channel A orchannel C without, however, affecting thedeviation range of modulation. Crystal controlled. frequency changes Without affecting this deviation frange is made' possible by this invention While utilizing only one crystal to effect a variety -of such frequency changes. v -Suitable ampliers may be used after the mixer stage to raise the output Voltage to a desired amplitude and multipliers may be used as desired to effect further frequency increases.

While I have. illustrated and described the output of the mixer stages as being tuned to select the additive beat'frequencies, it is apparent that the system is flexible enough to conform to many requirements such as the selection of the differchannels and under the control of said source for generating Waves having a fundamental frequency which is a submultiple of the frequency of said source and rich in harmonics of saidzsubmultiple frequency, means connected solely to the output of said last named means to lter any one of a series of contiguous submultiple harmonies within a, first frequency band which is higher than the frequency of `said source, means in the other of said channels and controlled by said source for generating a wave having a frequency which is a multiple of the frequency of said source and which is higher than any of the harmonics in said first band and displaced therefrom by an interval which is equal to at least several times the frequency of said source, and

a mixer energized by a selected harmonic in the first channel and the multiple frequency output of said second channel` 2. A high frequency alternating current system comprising a pair of channels fed in parallel from a source of alternating current, means in one of said channels and under the control` of said source for generating waves having a fundamental frequency which is a submultiple of the frequency of said source and rich in` harmonies of said submultiple frequency, means connected solely vto the output of said last-named means tc select any one of a series of contiguous submultiple harmonics within a first frequency band which is higher than the frequency of said source, means in the other of said channels and controlled :by the output of said source to generate a plurality of Waves having frequencies which are multiples of the frequency of said source, said multiples lying in a second frequency band which is displaced from said first frequency band by an interval which is equal to at least several times the frequency of said source, and a mixer energized by a Selected harmonic in the first channel and a predetermined multiple in said second channel to derive beat frequencies of` the currents fed therein, and means to select one `said beat frequencies.

3. A high frequency alternating current generf ating system comprising in combination a. relatively stable source of sine Wave oscillations, a pair of mutually independent channels fed from said source, a non-sinusoidal Wave generator in one of said channels and under the control of said oscillations for generating Waves having a fundament-al frequency which is a submultiple of the frequency of said oscillations, means connected solely to the output of said generator to select and amplify any one of a series of contiguous harmonics of `said submultiple frequency lying within a first frequency band which is l higher than the frequency of said source, means in the other of said channels and controlled byA the output of said source for generating a plurality of waves having frequencies which are imultiples of the frequency of said source, said `multiples lying in a second frequency band which is `higher than said first :band and displaced therefrom by an interval which is equal to at least several times the frequency of said source,

the width of said first band being at least equal to the frequency of said source, a mixer energized by a selected harmonic in the first channel and a predetermined multiple in said other channel to derive beat frequencies of the currents fed therein, and means to tune said mixer to select one said beat frequencies.

4. A high frequency alternating current gen` erating system comprising in combination a stabilized source of sine Wave oscillations, a pair of `mutually independent channels fed from said source, a multivibrator in one of said channels and under the control of said source for generating Waves having a fundamental frequency which is -a swbmultiple of the frequency of said oscillations, means connected solely to the output of said multivibrator to filter and amplify any one of a series of contiguous harmonics of said su=b multiple frequency lying Within a first frequency I band which is higher than the frequency of said source, a frequency doubler under the control of said source inthe other of said channels,v

means controlled by the output of said doubler to generate a pluralityof Waves having frequencies Which are multiples of the frequency of the output of said doubler, said multiples lying in a second frequency band which is higher than said rst band and displaced therefrom by an interval which is equal to at least several times the lfrequency of said source,` the width of said first band being at least equal to the interval between to tune said mixer to select one said beat frequencies.

i WILLIAM S. MARKS, JR. 

